The projects that we present in this grant proposal deal with the study of the molecular events that occur both during electrical excitation in nerve and muscle and during active transport of ions which lead to the recovery of the normal ionic gradients across the cell membrane. To accomplish these goals, we propose to use artificial lipid membranes as model systems. The first project will involve the reconstitution of the membrane-bound enzyme, (Na ion plus K ion) activated ATP-ase, as well as the membrane-bound glycoprotein. This part of the project is described in the section entitled "Incorporation of functional membrane proteins into lipid bilayers." In the second project, the molecular events underlying the process of excitability will be studied using the model system hemocyanin-lipid bilayer. This part of the project is described in the section entitled "Nature of the Voltage-Dependent Conductance in Membranes." The third project will be devoted to study the relations between the primary structure and transport properties of ion carriers and the effect of changes in membrane composition on ion transport. This part of the project is described in the section entitled "On carrier mediated ion transport, selectivity and membrane composition."